Phased arrays of antenna elements are commonly used in radar and other applications in which a direction of an incoming radio frequency (RF) signal needs to be ascertained or in which an RF signal needs to be transmitted in a particular direction. One or more receivers, transmitters or transceivers are electrically connected to an array of antenna elements via feed lines, such as waveguides or coaxial cables. Taking a transmitter case as an example, the transmitter(s) operate such that the phase of the signal at each antenna element is separately controlled. Signals radiated by the various antenna elements constructively and destructively interfere with each other in the space in front of the antenna array. In directions where the signals constructively interfere, the signals are reinforced, whereas in directions where the signals destructively interfere, the signals are suppressed, thereby creating an effective radiation pattern of the entire array that favors a desired direction. The phases at the various antenna elements, and therefore the direction in which the signal propagates, can be changed very quickly, thereby enabling such a system to be electronically steered, for example to sweep over a range of directions.
According to the reciprocity theorem, a phased array of antenna elements can be used to receive signals preferentially from a desired direction. By electronically changing the phasing, a system can sweep over a range of directions to ascertain a direction from which a signal originates, i.e., a direction from which the signal's strength is maximum, or to electronically steer a phased array toward a transmitting antenna and away from interference (noise) sources.
Phased arrays are physically large, relative to wavelengths of signals transmitted and/or received by the arrays. Many phased arrays are also massive. Consequently, launching phased arrays into outer space, or constructing such arrays in space, is difficult or impossible with current launch vehicles and space construction techniques.